I've used a couple of different methods in the past;
For the wheels on my homemade bandsaw I wasn't worried about colour, just durability. I soaked the edges of the MDF with a 50/50 mixture of danish oil and oil based varnish, this thin mixture soaked into the edge grain really easily. I did have to apply it about 3 times for the first coat as the material just kept sucking it up. This was intentional however as I wanted the varnish to get deep into the fibres and bind them together to increase durability. I think I did three coats in total, gradually increasing the proportion of varnish in the oil/varnish mixture. I sanded the edges back with 180 and 240 between coats.
For painted items I use a waterbased paint system from Wickes, it's in their trade range and comes in 5l tins.
Supreme Grip Primer, Trade Undercoat & Truewhite Liquid Gloss.
Primer Coat
I only sand the edges of the MDF if I need to flush up a joint, if they are already flush I go straight to the primer getting a heavy coat over everything. If the edges suck up the paint I apply it a second time and set it aside to dry. Once fully dry I sand with 180 or 240 to knock down the nibs and any fluffy raised grain, I don't worry about sanding through this layer as I just want the surface smooth. At this point the exposed edge grain fibres are bound together and not able to absorb any more paint. I then put on another coat of primer and make sure this is smoothly applied and tipped off.
Undercoat
Lightly sand the dried second primer coat with 240 to knock back the dust nibs. I then vacuum and wipe down to get rid of any particles stuck to the surface before applying a coat of undercoat. This builds the paint thickness and flows out nicely but you cant go over areas if it has started to dry as it'll just drag on the surface making a mess.
Gloss
Again denib with 240, vacuum, wipe down and then examine the surface carefully. The gloss layer is only very thin so whatever surface you have now will be reflected through to the finished surface. As there is plenty of material in the undercoat layer you can sand away until it is how you want it. The gloss needs to be applied quickly with a roller and then tipped off with a good brush, if it starts to dry don't touch it or like the undercoat you'll just make it worse. One coat of the gloss should be enough but you can do more if you have the patience.
For the wheels on my homemade bandsaw I wasn't worried about colour, just durability. I soaked the edges of the MDF with a 50/50 mixture of danish oil and oil based varnish, this thin mixture soaked into the edge grain really easily. I did have to apply it about 3 times for the first coat as the material just kept sucking it up. This was intentional however as I wanted the varnish to get deep into the fibres and bind them together to increase durability. I think I did three coats in total, gradually increasing the proportion of varnish in the oil/varnish mixture. I sanded the edges back with 180 and 240 between coats.
For painted items I use a waterbased paint system from Wickes, it's in their trade range and comes in 5l tins.
Supreme Grip Primer, Trade Undercoat & Truewhite Liquid Gloss.
Primer Coat
I only sand the edges of the MDF if I need to flush up a joint, if they are already flush I go straight to the primer getting a heavy coat over everything. If the edges suck up the paint I apply it a second time and set it aside to dry. Once fully dry I sand with 180 or 240 to knock down the nibs and any fluffy raised grain, I don't worry about sanding through this layer as I just want the surface smooth. At this point the exposed edge grain fibres are bound together and not able to absorb any more paint. I then put on another coat of primer and make sure this is smoothly applied and tipped off.
Undercoat
Lightly sand the dried second primer coat with 240 to knock back the dust nibs. I then vacuum and wipe down to get rid of any particles stuck to the surface before applying a coat of undercoat. This builds the paint thickness and flows out nicely but you cant go over areas if it has started to dry as it'll just drag on the surface making a mess.
Gloss
Again denib with 240, vacuum, wipe down and then examine the surface carefully. The gloss layer is only very thin so whatever surface you have now will be reflected through to the finished surface. As there is plenty of material in the undercoat layer you can sand away until it is how you want it. The gloss needs to be applied quickly with a roller and then tipped off with a good brush, if it starts to dry don't touch it or like the undercoat you'll just make it worse. One coat of the gloss should be enough but you can do more if you have the patience.
